The Nervous System. The master controlling and communication system of The master controlling and communication system of the body.

The Nervous The Nervous SystemSystem

The Nervous The Nervous SystemSystem

The master The master controlling controlling and and communicacommunication system tion system ofof

the bodythe body

Three Overlapping Three Overlapping FunctionsFunctions

Sensory InputSensory Input Monitors internal and external stimuli Monitors internal and external stimuli

(Changes)(Changes) Afferent pathway to the brainAfferent pathway to the brain receptorsreceptors

IntegrationIntegration Processes and interprets informationProcesses and interprets information Decides the appropriate responseDecides the appropriate response

Motor OutputMotor Output Efferent pathway to effector organs Efferent pathway to effector organs

(muscles or glands), effects a response(muscles or glands), effects a response

Organization of the Organization of the Nervous SystemNervous System

Central Nervous SystemCentral Nervous System (CNS) (CNS) Brain and spinal cordBrain and spinal cord Dorsal body cavityDorsal body cavity Integrating command centerIntegrating command center

Peripheral Nervous SystemPeripheral Nervous System (PNS) (PNS) Nerves to and from brain and spinal Nerves to and from brain and spinal

cordcord Communication links to the CNSCommunication links to the CNS Spinal nerves and cranial nervesSpinal nerves and cranial nerves

Peripheral Nervous SystemPeripheral Nervous System

Sensory Afferent DivisionSensory Afferent Division Impulses to the brain and spinal cord Impulses to the brain and spinal cord

(CNS)(CNS) Monitors internal and external changesMonitors internal and external changes Somatic afferentSomatic afferent

Skin, skeletal muscle, jointsSkin, skeletal muscle, joints Visceral afferentVisceral afferent

Organs within ventral body cavityOrgans within ventral body cavity

Peripheral Nervous SystemPeripheral Nervous System Motor Efferent DivisionMotor Efferent Division

From CNS to effector muscle, organs, and From CNS to effector muscle, organs, and glandsglands

Somatic efferent nervous systemSomatic efferent nervous system Voluntary nervous systemVoluntary nervous system

Autonomic nervous systemAutonomic nervous system InvoluntaryInvoluntary Visceral motor nerve fibers (to smooth and cardiac Visceral motor nerve fibers (to smooth and cardiac

muscle and glands)muscle and glands) Sympathetic (emergency situations)Sympathetic (emergency situations) Parasympathetic (conserves energy, nonemergency Parasympathetic (conserves energy, nonemergency

functions)functions)

ClassificationClassification P. 224P. 224

Nervous SystemNervous System

THE CELLS OF THE THE CELLS OF THE NERVOUS SYSTEMNERVOUS SYSTEM

Nervous Tissue-Types of CellsNervous Tissue-Types of CellsTwo Principal Cell Types-Two Principal Cell Types- NeuronsNeurons: excitable nerve cells: excitable nerve cells Supporting cellsSupporting cells: : Neuroglia “Nerve Glue”Neuroglia “Nerve Glue”

Support, insulate, and protect neurons by Support, insulate, and protect neurons by surrounding and wrapping neurons.surrounding and wrapping neurons.

Central nervous system supporting cellsCentral nervous system supporting cells AstrocytesAstrocytes MicrogliaMicroglia Ependymal cellsEpendymal cells OligodendrocytesOligodendrocytes

Peripheral nervous system supporting cellsPeripheral nervous system supporting cells Satellite cellsSatellite cells Schwann cellsSchwann cells

Neuroglia-Neuroglia-Supporting Cells Supporting Cells

of CNSof CNS

AstrocytesAstrocytes Most abundantMost abundant *Star-shaped*Star-shaped Radiating processes cover neurons and anchor Radiating processes cover neurons and anchor

them to adjacent blood vesselsthem to adjacent blood vessels Controls exchange between blood vessels and Controls exchange between blood vessels and

neuronsneurons Determines capillary permeabilityDetermines capillary permeability

Astrocytes (Cont)Astrocytes (Cont) Controls chemical environment around Controls chemical environment around

neuronsneurons Cleans up leaked potassium and recycling Cleans up leaked potassium and recycling

released neurotransmitterreleased neurotransmitter Guide migration of young neuronsGuide migration of young neurons

MicrogliaMicroglia Small, ovoid cells, with thorny processes Small, ovoid cells, with thorny processes

(spider-like)(spider-like) Branches monitor health of neuronsBranches monitor health of neurons Migrate toward injured neuronMigrate toward injured neuron Transform into a macrophage when invading Transform into a macrophage when invading

microorganisms or dead neurons are present microorganisms or dead neurons are present and and disposedispose of debris of debris

Protective role because cells of immune Protective role because cells of immune system are denied access to CNSsystem are denied access to CNS

Ependymal cellsEpendymal cells

Simple squamous to columnar in shapeSimple squamous to columnar in shape Line the cavities of the brain and spinal Line the cavities of the brain and spinal

cordcord Beating of their cilia circulates Beating of their cilia circulates

cerebrospinal fluid that cushions brain cerebrospinal fluid that cushions brain and spinal cordand spinal cord

OligodendrocytesOligodendrocytes

Wrap cytoplasmic extensions around Wrap cytoplasmic extensions around neurons and form neurons and form myelin sheaths in myelin sheaths in CNSCNS

Insulates and protectsInsulates and protects

Supporting Cells of the PNSSupporting Cells of the PNS

Satellite cellsSatellite cells Surround neuron cell bodies within gangliaSurround neuron cell bodies within ganglia Protective and cushioning cellsProtective and cushioning cells

Schwann cellsSchwann cells Surround and form myelin sheaths around Surround and form myelin sheaths around

larger nerve fiberslarger nerve fibers Functionally similar to oligodendrocytesFunctionally similar to oligodendrocytes

NeuronsNeurons

Highly specialized to transmit Highly specialized to transmit nerve impulsesnerve impulses

NeuronsNeurons Nerve cellsNerve cells Structural units of the nervous systemStructural units of the nervous system Special characteristics of neurons:Special characteristics of neurons:

1.1. Conduct nerve impulsesConduct nerve impulses2.2. Extreme longevityExtreme longevity3.3. Amiotic (exceptions: olfactory and hippocampus) Amiotic (exceptions: olfactory and hippocampus)

(become injured and do not regenerate)(become injured and do not regenerate)4.4. High metabolic rate: requires abundant oxygen High metabolic rate: requires abundant oxygen

and glucoseand glucose All Neurons have All Neurons have cell bodies cell bodies and and processesprocesses, ,

plus three functional components: receptive plus three functional components: receptive or input region, conducting component, and or input region, conducting component, and secretory or output component.secretory or output component.

Cell BodyCell Body Metabolic centerMetabolic center No centriolesNo centrioles Ribosomes and rough ER (Ribosomes and rough ER (NisslNissl

SubstanceSubstance)most active of any cell in the )most active of any cell in the bodybody

Plasma membrane acts as part of the Plasma membrane acts as part of the receptive surfacereceptive surface

Most located within the CNS (called Most located within the CNS (called nucleinuclei))

Cell body collections in the PNS are called Cell body collections in the PNS are called gangliaganglia

Cell ProcessesCell Processes Brain and spinal cord (CNS) contain both Brain and spinal cord (CNS) contain both

cell bodies and their processescell bodies and their processes The PNS consists chiefly of neuron The PNS consists chiefly of neuron

processesprocesses Bundles of neuron processes are calledBundles of neuron processes are called

tracts tracts (CNS) and (CNS) and nervesnerves (PNS). (PNS). DendritesDendrites

Short, tapering, hundreds/cellShort, tapering, hundreds/cell Receptive (input) region; convey incoming Receptive (input) region; convey incoming

messages(electrical signals) toward the cell messages(electrical signals) toward the cell bodybody

Large surface area Large surface area

Cell ProcessesCell ProcessesAxonAxon (conducting component)(conducting component)

One Axon (Single process) per neuronOne Axon (Single process) per neuron Axon arises from Axon arises from axon hillock axon hillock of cell body of cell body Generates nerve impulses and transmits Generates nerve impulses and transmits

them away from the cell bodythem away from the cell body Long axons called nerve fibersLong axons called nerve fibersAxon terminals –Axon terminals –created where the axon created where the axon

branches at the terminal end branches at the terminal end 100-1000+ terminal branches per 100-1000+ terminal branches per

axon axon Axon terminals are the secretory portion—Axon terminals are the secretory portion—

secretes neurotransmitterssecretes neurotransmitters

Myelin SheathMyelin Sheath (neurilemma)(neurilemma)

MyelinMyelin: whitish, fatty material covering long : whitish, fatty material covering long nerve fibers; has waxy appearancenerve fibers; has waxy appearance

Protects and provides an electrical insulation Protects and provides an electrical insulation covering for large and long nerve fiberscovering for large and long nerve fibers

Increases speed of transmission of nerve Increases speed of transmission of nerve impulsesimpulses

Unmyelinated fibers conduct impulses slowlyUnmyelinated fibers conduct impulses slowly Associated only with axons; Dendrites always Associated only with axons; Dendrites always

unmyelinatedunmyelinated Formed by Formed by Schwann cells Schwann cells in PNS—made of in PNS—made of

concentric layers of cell membranes (no concentric layers of cell membranes (no channel or carrier proteins) called the channel or carrier proteins) called the neurilemmaneurilemma

Myelin (Cont)Myelin (Cont) Nodes of Ranvier Nodes of Ranvier are the gaps between are the gaps between

Schwann cells—regularly spacedSchwann cells—regularly spaced OligodendrocytesOligodendrocytes form CNS myelin sheaths— form CNS myelin sheaths—

coils around 60 fibers at the same time—no coils around 60 fibers at the same time—no neurilemma because of the absence of coiling neurilemma because of the absence of coiling of cellsof cells

Regions of the brain and spinal cord with Regions of the brain and spinal cord with myelinated fibers called myelinated fibers called white matter. white matter.

Gray matter Gray matter contains mostly cell bodies and contains mostly cell bodies and unmyelinated fibersunmyelinated fibers

Classification of NeuronsClassification of Neurons Structural ClassificationStructural Classification

Multipolar neuronsMultipolar neurons Bipolar neuronsBipolar neurons Unipolar NeuronsUnipolar Neurons

Functional ClassificationFunctional Classification Sensory (afferent) neuronsSensory (afferent) neurons Motor (efferent) neuronsMotor (efferent) neurons Association (interneurons) neuronsAssociation (interneurons) neurons

Nervous Tissue Nervous Tissue StructuresStructures

p. 227p. 227

CELL BODY

DENDRITE

Nervous Tissue Nervous Tissue StructuresStructures

AXON

AXON TERMINAL

Nervous Tissue Nervous Tissue StructuresStructures

SCHWANN CELLS

NODES OF RANVIER